The objective of this research project is to study the heterogeneity of blood flow in the mammalian intestine and its relation to function with special attention paid to the microcirculation in the mucosa. In brief, microspheres (3M) (8 microns in dia. and larger) were injected into the left ventricle of animals which were then sacrificed. Intestinal segments were moved and cleared in methyl salicylate. Flow rate per bead was obtained by the reference organ method. In several experiments vascular casts of the intestine were made by latex injection. The cleared tissue was examined under the microscope to locate, count, and size the individual trapped beads. The method provides villus-to-villus and intravillus spatial resolution not now obtainable (or with much greater difficulty) by other available means, and when used together with morphological data, it can yield detailed information on the functional architecture of the microcirculation and its control. Work thus far has characterized the circulation to the dog small intestine in the post-absorptive state taken as a standard. It is proposed among other things to obtain data on other functional states such as during vasodilitation. It is also planned to relate spatial heterogeneity of flow to local rates of absorption of test solutes, to study temporal heterogeneity of flow, and to relate spatial heterogeneity of flow to the architecture of the microcirculation.